Conventionally, an image forming apparatus such as an electrophotographic copying machine uses a developer of fine particles. In such an image forming apparatus, the developer is supplied from the developer supply container in response to consumption thereof resulting from image forming operation.
Such a developer supply container is disclosed in Japanese Laid-open Patent Application 2010-256894, for example.
The apparatus disclosed in Japanese Laid-open Patent Application 2010-256894 employs a system in which the developer is discharged using a bellow pump provided in the developer supply container. More particularly, the bellow pump is expanded to provide a pressure lower than the ambient pressure in the developer supply container, so that the air is taken into the developer supply container to fluidize the developer. In addition, the bellow pump is contracted to provide a pressure higher than the ambient pressure in the developer supply container, so that the developer is pushed out by the pressure difference between the inside and the outside of the developer supply container, thus discharging the developer. By repeating the two steps alternately, the developer is stably discharged.